Lithium nickel ferrite magnetic switching element



United States Patent 3,376,227 LITHIUM NICKEL FERRITE MAGNETIC SWITCHING ELEMENT Gerrit Antonie Herman van Driel, 'Cornelis Jacobus Esveldt, and Johannes Engelmundus Joosten, Emmasingei, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed June 18, 1964, Ser. No. 376,238 Claims priority, application Netherlands, June 20, 1963, 294,371 4 Claims. (Cl. 252-62.61)

Our invention relates to magnetic cores for use as a magnetic switching element for controlling core storages, and particularly to a process of making the same.

Magnetic cores having a hysteresis loop approaching the form of a rectangle have various uses. Such cores are employed inter alia for so-called magnetic storage. Such magnetic storages are used inter alia in computers and automatic pilots. These cores are also employed in magnetic switches, and the present invention relates to the manufacture of cores particularly suitable for the lastmentioned use.

When magnetic cores are used as storage elements or magnetic switching elements, it is desirable to restrict, as far as possible, the appearance of eddy currents. Consequently, such cores are usually constituted of soft-magnetic, oxidic materials, which, as is known, have a very low electrical conductivity.

The invention relates to a method of manufacturing an annular magnetic core having an outer diameter of 2.8 to 4 mms., an inner diameter of at least 0.6-times the outer diameter and a height of 1 to 2 mms. for use as a magnetic switching element for controlling core storages. The particular suitability of the magnetic cores manufactured by the method according to the invention as magnetic switching elements is based on the combination of the following properties:

(a) uVl (measured with a control-current intensity of 2 a.) exceeds 1000 mv.;

(b) uVz (measured with a control-current intensity of 1.8 a. and a rise time of 0.25 ,usec.) is lower than 40 mv.; and

exceeds 0.9.

The symbols uVl and uVz are understood to have the following meaning:

uVl (undisturbed voltage one) is the maximum value of the undisturbed one signal with the given controlcurrent intensity as a function of time, calculated from the beginning of the particular control-current pulse.

The magnitude uVz (undisturbed voltage zero) is the maximum value of the voltage pulse with the given control-current intensity and the given rise time, at which the magnetic core passes from one of the two states of remanent inductance to the state of maximum inductance, which has the same sign as the relevant remanent inductance.

In order to determine the numerical value of the magnitude R, uVl is measured with two different intensities of the control-current 1, i.e., with the values I=1.8 a. and I=2.1 a. The difference between the two measured values of uVl is designated by the symbol AuVl, where AI has the value of 2.1 a.1.8 a. =0.3 a.

The magnet cores, according to the invention, are prepared in accordance with a process in which a finelydivided mixture of Mol percent Li O l4l5 NiO 67 Fe O 77-81 is presintered at a temperature of 600 to 750 C., the product thus obtained being refined, subsequently granulated and molded by compression into a body having the approximate dimensions of the magnet core. This compressed body is heated to a temperature of 1370 C. to 1400 C. within a period of not more than 16 minutes, and is maintained at that temperature for 5 to 10 minutes. The body then is -cooled to a temperature of 940 C. to 960 C. within a period of 70 to 90 minutes, and finally quenched by direct contact with air at ambient temperature.

In a preferred embodiment of the method, according to the invention, the above-mentioned compressed body is heated to a temperature of 1300 C. to 1310 C. within 2 to 4 minutes, after which the temperature is raised to 1380 C. to 1390 C. within 8 to 10 minutes. The body is maintained at this latter temperature for 6 to 8 minutes, after which the reaction product is cooled to a temperature of 945 C. to 955 C. within a period of to minutes. The product is finally quenched by direct contact with air at ambient temperature.

It should be understood that where oxides are specified, both herein and in the claims, compounds which decompose to form oxides upon heating may be used instead.

The following examples are illustrative only of the invention which is defined with greater particularity in the appended claims.

EXAMPLE I A mixture of 14.5 mol percent of lithium carbonate, Li CO 6.45 mol percent of nickel carbonate, NiCO and 79.05 mol percent of iron oxide, Fe O was ground with ethanol as a grinding liquid in a ball mill for 4 hours. The grinding product was presintered at 700 C. to 750 C. for one hour, cooled and then ground with ethanol as a grinding liquid in a ball mill for 16 hours, after which an organic binder was added to the ground product. The mass was then granulated by means of a sieve of fine mesh and compressed in the form of rings having an outer diameter of 3.75 mms., an inner diameter of 2.5 mms. and a height of 1.95 mms.

The annular compressed bodies were heated to a temperature of 1390 C. within 3 minutes by introducing them on a platinum shuttle into a previously switched-on furance. They were then sintered at said temperature for 7 minutes, after which the furnace temperature was reduced to 950 C. in the course of 85 minutes. After the sintered bodies had been cooled in and with the furnace to 950 C., they were removed from the furnace and quenched by direct contact with air at room temperature.

The following pulse characteristics were measured on the ferrite rings thus obtained:

uVl (control-current intensity I=1.8 a.)'=840 m'v. uVl (control-current intensity I=2.1 a.)=1140 mv.

(It follows therefrom AuVl R AI =1.0 ohm) A mixture of the same composition as specified in Example I was worked up in the manner described in said example to obtain compressed bodies having an outer diameter of 3.75 mms. an inner diameter of 2.50 mms. and a height of 1.95 mms.

In the course of 3 minutes, the annular compressed bodies were heated to a temperature of 1305 C. by introducing them on a platinum shuttle into a furnace previously switched on. The furnace temperature was then raised to 1384" C. within 9 minutes and this temperature was maintained for 7 minutes. Then, in the course of 80 minutes, the furnace temperature was reduced to 950 C. Thereafter, the annular sintered bodies were cooled in and with the furnace and quenched by direct contact with air at ambient temperature. The following pulse characteristics were measured on the ferrite rings thus obtained:

(It follows therefrom AuVl AI -1.1 ohms) The outer diameter of the ferrite rings was 3.0 mms., the inner diameter 2.0 nuns. and the height 1.55 mms.

What we claim is:

1. A method of manufacturing an annular magnetic core having an outer diameter of about 2.8 to 4 mms., an inner diameter of at least 0.6 times the outer diameter, and a height of about 1 to 2 turns, for use as a switching element for controlling core storages comprising the steps, forming a finely-divided mixture of about 14 to 15 mol percent of Li O, about 6 to 7 mol percent of NiO, and about 77 to 81 mol percent of Fe O compressing said mixture into an annular body having approximately the said dimensions, heating said annular body to a temperature of about 1370 C. to 1400 C. within not more than 16 minutes, maintaining said annular body at said temperature for about 5 to 10 minutes, cooling said body to a temperature of about 940 C. to 960 C. within a period of time thereafter bringing said body into direct contact with air at ambient temperature to quench the same.

2. A method of manufacturing an annular magnetic core having an outer diameter of about 2.8 to 4 mms., an inner diameter of at least 0.6 times the outer diameter, and a height of about 1 to 2 ms, for use as a switching element for controlling core storages comprising the steps, forming a finely-divided mixture of about 14 to 15 mol. percent of M 0, about 6 to 7 mol percent of NiO, and about 77 to 81 mol percent of 1512 0 compressing said mixture into an annular body having approximately the said dimensions, heating said annular body to a temperature of 1300 C. to 1310 C. Within 2 to 4 minutes, heating said 'body from said temperature to a temperature of 1380 C. to 1390 C. within 8 to 10 minutes, maintaining said body at said latter temperature for 6 to 8 minutes, cooling said body to a temperature of 945 C. to 955 C. in to 85 minutes, and finally bringing said body into direct contact with air at ambient temperature to quench the same.

3. An annular magnet core made in accordance with the process defined in claim 1.

4. An annular magnet core made in accordance with the process defined in claim 2.

References Cited UNITED STATES PATENTS 3,038,860 6/1962 Vinal et a1. 252-625 3,226,328 12/1965 Esveldt et a1 252,-62.5

TOBIAS E. LEVOW, Primary Examiner.

ROBERT D. EDMONDS, HELEN MCCARTHY,

Examiners.

of about 70 to minutes, and finally, 

1. A METHOD OF MANUFACTURING AN ANNULAR MAGNETIC CORE HAVING AN OUTER DIAMETER OF ABOUT 2.8 TO 4 MMS., AN INNER DIAMETER OF AT LEAST 0.6 TIMES THE OUTER DIAMETER, AND A HEIGHT OF ABOUT 1 TO 2 MMS., FOR SUE AS A SWITCHING ELEMENT FOR CONTROLLING CORE STORAGES COMPRISING THE STEPS, FORMING A FINELY-DIVIDED MIXTURE OF ABOUT 14 TO 15 MOL PERCENT OF LI2O, ABOUT 6 TO 7 MOL PERCNT OF NIO, AND ABOUT 77 TO 81 MOL PERCENT OF FE2O3, COMPRESSING SAID MIXTURE INTO AN ANNULAR BODY HAVING APPROXIMATELY THE SAID DIMENSIONS, HEATING SAID ANNULAR BODY TO A TEMPERATURE OF ABOUT 1370*C. TO 1400*C. WITHIN NOT MORE THAN 16 MINUTES, MAINTAINING SAID ANNULAR BODY AT SAID TEMPERATURE FOR ABOUT 5 TO 10 MINUTES, COOLING SAID BODY TO A TEMPERATURE OF ABOUT 940*C. TO 960*C. WITHIN A PERIOD OF TIME OF ABOUT 40 TO 90 MINUTES, AND FINALLY THEREAFTER BRINGING SAID BODY INTO DIRECT CONTACT WITH AIR AT AMBIENT TEMPERATURE TO QUENCH THE SAME.
 3. AN ANNULAR MAGNET CORE MADE IN ACCORDANCE WITH THE PROCESS DEFINED IN CLAIM
 1. 